Hydrophone is a microphone designed for recording or listening to underwater sound. Most hydrophones are based on piezoelectric transducers that generate electricity when subjected to a pressure change of sound wave (acoustic energy). Hydrophone helps in detecting or monitoring sound under water. Applications of hydrophones include aquarium audio products, Hydrophone networks for SeaSound effects analysis, marine survey, sea navigation systems, deep ocean research, sea-phone, underwater ultrasonic transducers, tracking of marine fish and wildlife, and sound detection in liquids.

Hydrophones are similar to microphones except they operate in water instead of air; so you could call them underwater microphones. Hydrophone can “listen” to sound in air, but will be less sensitive due to its design as having a good acoustic impedance match to water, the denser fluid.

Important features of hydrophones are low noise, good sensitivity, broadband frequency range, optional integral electrostatic shield, optional pre-amplifiers. Omnidirectional hydrophones increase reception sensitivity from one direction using two basic techniques: Focused Hydrophone Transducers, and Hydrophone arrays.

Hydrophones measure underwater sound such as that created by whales, dolphins, or even shrimp. They are also useful for underwater noise analysis and have industrial applications, such as monitoring pile driver noise or measuring the underwater sound pressure level created by air gun arrays. Broadband low-noise Hydrophones increases the sensitivity of underwater sound detection. Underwater echo detection systems were developed for the purpose of underwater navigation by submarines.